Inkjet Nozzle Arrangement With Electro-Thermally Actuated Lever Arm

ABSTRACT

A nozzle arrangement is provided for an inkjet printhead. The nozzle arrangement includes a substrate assembly, in turn, including an electrical drive circuitry layer and defining an ink inlet channel. A nozzle chamber structure extends from the substrate assembly. The nozzle chamber structure defines a nozzle chamber in fluid communication with the ink inlet channel and an ink ejection port in fluid communication with the nozzle chamber. An anchor extends from the substrate assembly. A thermal bend actuator extends from the anchor and is electrically coupled to the drive circuitry layer. A lever arm is coupled to the thermal bend actuator, is pivotally supported by the substrate assembly and terminates in a paddle within the nozzle chamber. Upon receipt of a driving signal from the drive circuitry layer, the thermal bend actuator bends to induce movement of the paddle and ejection of ink in the nozzle chamber through the ink ejection port.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a Continuation application of U.S.application Ser. No. 10/510,153 filed on Oct. 5, 2004, which is a 371 ofPCT/AU02/00762 filed on Jun. 13, 2002, which is a continuation of U.S.application Ser. No. 10/120,347 filed on Apr. 12, 2002, now issued U.S.Pat. No. 6,540,332, which is a continuation in part of U.S. applicationSer. No. 09/112,767 filed on Jul. 10, 1998, now issued U.S. Pat. No.6,416,167 all of which are herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a printhead chip. More particularly, thisinvention relates to a printhead chip that incorporates a plurality ofnozzle arrangements that each include a motion transmitting structure.

BACKGROUND OF THE INVENTION

As set out in the above referenced applications/patents, the Applicanthas spent a substantial amount of time and effort in developingprintheads that incorporate micro electromechanical system (MEMS)-basedcomponents to achieve the ejection of ink necessary for printing.

As a result of the Applicant's research and development, the Applicanthas been able to develop printheads having one or more printhead chipsthat together incorporate up to 84 000 nozzle arrangements. TheApplicant has also developed suitable processor technology that iscapable of controlling operation of such printheads. In particular, theprocessor technology and the printheads are capable of cooperating togenerate resolutions of 1600 dpi and higher in some cases. Examples ofsuitable processor technology are provided in the above referencedpatent applications/patents.

Common to most of the printhead chips that the Applicant has developedis a component that moves with respect to a substrate to eject ink froma nozzle chamber. This component can be in the form of an ink-ejectingmember that is displaceable in a nozzle chamber to eject the ink fromthe nozzle chamber.

A particular difficulty that the Applicant has been faced with is toachieve a suitable interface between a prime mover in the form of anactuator and the moving component. This interface is required to permitthe moving component to be displaced in the nozzle chamber and toinhibit leakage of ink from the nozzle chamber.

As set out in the above referenced patents/patent applications, theprinthead chip is manufactured using integrated circuit fabricationtechniques. This is the usual manner in which MEMS-based devices arefabricated. Such forms of fabrication are subject to constraints sincethey involve successive deposition and etching techniques. It followsthat MEMS-based devices are usually formed in layers and that componentshaving relatively complex shapes are difficult and expensive tofabricate.

In FIG. 1, reference numeral 10 generally indicates part of a nozzlearrangement of a printhead chip. The part 10 shown illustrates anactuator 12 and an ink-ejecting member 14. The actuator 12 includes anelongate actuator arm 16 that extends from an anchor 18. The actuatorarm 16 is configured so that, when it receives a drive signal, theactuator arm 16 bends towards a substrate 20 as indicated by an arrow22. A connecting formation 24 is interposed between the actuator arm 16and the ink-ejecting member 14. Thus, when the actuator arm 16 is benttowards the substrate 20, the ink-ejecting member 14 is displaced in thedirection of an arrow 26 to eject ink from the nozzle chamber.

It would be intuitive simply to use the arrangement 10 together with asuitable sealing structure to achieve effective ink ejection andsealing. The reason for this is that it would appear that the actuatorarm 16, the connecting formation 24 and the ink-ejecting member 14 couldbe in the form of a unitary structure. However, the Applicant has foundthat it is not possible to achieve a working configuration as shown byusing MEMS-based fabrication techniques. In particular, it has beenfound by the Applicant that such a unitary structure does not lenditself to such fabrication techniques.

It follows that the Applicant has been led to conceive the presentinvention.

SUMMARY OF THE INVENTION

According to the invention, there is provided a printhead chip for aninkjet printhead, the printhead chip comprising

a substrate; and

a plurality of nozzle arrangements positioned on the substrate, eachnozzle arrangement comprising

-   -   a nozzle chamber structure that defines a nozzle chamber in        which ink is received;    -   an ink-ejecting member that is positioned in the nozzle chamber        and is displaceable in the nozzle chamber to eject ink from the        nozzle chamber;    -   at least one actuator that is positioned on the substrate, the,        or each, actuator having a working portion that is displaceable        with respect to the substrate when the actuator receives a        driving signal;    -   a sealing structure that is positioned on the substrate and is        interposed between the, or each, actuator and the ink-ejecting        member to inhibit a passage of ink between the ink-ejecting        member and the actuator; and    -   a motion transmitting structure that bridges the sealing        structure, the motion transmitting structure interconnecting the        working portion of the actuator and the ink-ejecting member so        that displacement of the working portion relative to the        substrate is transmitted to the ink-ejecting member.

The invention is now described, by way of example, with reference to theaccompanying drawings. The following description is not intended tolimit the broad scope of the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 shows a schematic side sectioned view of part of a nozzlearrangement of a printhead chip for an inkjet printhead for the purposesof conceptual illustration;

FIG. 2 shows a schematic side sectioned view of a nozzle arrangement ofa first embodiment of a printhead chip, in accordance with theinvention, for an inkjet printhead;

FIG. 3 shows a three dimensional, side sectioned view of a nozzlearrangement of a second embodiment of a printhead chip, in accordancewith the invention, for an inkjet printhead; and

FIG. 4 shows a three dimensional view of the nozzle arrangement of FIG.3.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 2, reference numeral 30 generally indicates a nozzle arrangementof a first embodiment of an ink jet printhead chip, in accordance withthe invention, for an inkjet printhead.

The nozzle arrangement 30 is one of a plurality of such nozzlearrangements formed on a silicon wafer substrate 32 to define theprinthead chip of the invention. As set out in the background of thisspecification, a single printhead can contain up to 84 000 such nozzlearrangements. For the purposes of clarity and ease of description, onlyone nozzle arrangement is described. It is to be appreciated that aperson of ordinary skill in the field can readily obtain the printheadchip by simply replicating the nozzle arrangement 30 on the wafersubstrate 32.

The printhead chip is the product of an integrated circuit fabricationtechnique. In particular, each nozzle arrangement 30 is the product of aMEMS-based fabrication technique. As is known, such a fabricationtechnique involves the deposition of functional layers and sacrificiallayers of integrated circuit materials. The functional layers are etchedto define various moving components and the sacrificial layers areetched away to release the components. As is known, such fabricationtechniques generally involve the replication of a large number ofsimilar components on a single wafer that is subsequently diced toseparate the various components from each other. This reinforces thesubmission that a person of ordinary skill in the field can readilyobtain the printhead chip of this invention by replicating the nozzlearrangement 30.

An electrical drive circuitry layer 34 is positioned on the siliconwafer substrate 32. The electrical drive circuitry layer 34 includesCMOS drive circuitry. The particular configuration of the CMOS drivecircuitry is not important to this description and has therefore beenshown schematically in the drawings. Suffice to say that it is connectedto a suitable microprocessor and provides electrical current to thenozzle arrangement 30 upon receipt of an enabling signal from saidsuitable microprocessor. An example of a suitable microprocessor isdescribed in the above referenced patents/patent applications. Itfollows that this level of detail will not be set out in thisspecification.

An ink passivation layer 36 is positioned on the drive circuitry layer34. The ink passivation layer 36 can be of any suitable material, suchas silicon nitride.

The nozzle arrangement 30 includes a nozzle chamber structure 38. Thenozzle chamber structure 38 defines a nozzle chamber 40 and has a roof42 that defines an ink ejection port 44.

The nozzle chamber structure 38 includes a pair of opposed sidewalls 46,a distal end wall 48 and a proximal end wall 50 so that the nozzlechamber 40 is generally rectangular in plan.

A plurality of ink inlet channels 52 are defined through the siliconwafer substrate 32, the drive circuitry layer 34 and the ink passivationlayer 36. One ink inlet channel 52 is in fluid communication with eachrespective nozzle chamber 40. Further, each ink inlet channel 52 isaligned with each respective ink ejection port 44.

The nozzle arrangement 30 includes an ink-ejecting member in the form ofa paddle 54. The paddle 54 is dimensioned to correspond generally withthe nozzle chamber 40. Further, the paddle 54 has a distal end portion56 that is interposed between an opening 58 of the ink inlet channel 52and the ink ejection port 44. The paddle 54 is angularly displaceablewithin the nozzle chamber 40 so that the distal end portion 56 can movetowards and away from the ink ejection port 44. Thus, when the nozzlechamber 40 is filled with ink 60, such movement of the paddle 54 resultsin a fluctuation of ink pressure within the nozzle chamber 40 so that anink drop 62 is ejected from the ink ejection port 44. The mechanism ofink drop ejection is fully set out in the above referenced applicationsand patents. It follows that this detail is not set out in thisspecification.

The nozzle arrangement 30 includes an actuator in the form of a thermalbend actuator 64. This form of actuator is also described in the abovereferenced applications and patents and is therefore not described infurther detail in this specification. Briefly, however, the thermal bendactuator 64 includes an actuator arm 66 that has a fixed end 68 that isfixed to an anchor 70 and a working end 72 that is displaceable towardsand away from the substrate 32 upon receipt of a drive signal in theform of a current pulse emanating from the drive circuitry layer 34.

The nozzle arrangement 30 includes a sealing structure 78 that isinterposed between the working end 72 of the actuator arm 66 and aproximal end portion 76 of the paddle 54. The actuator arm 66, thesealing structure 78 and the paddle 54 are the product of a depositionand etching process carried out with a single material. However, the arm66, the sealing structure 78 and the paddle 54 are discrete components.This facilitates fabrication of the nozzle arrangement 30.

The material can be any of a number of materials used in integratedcircuit fabrication processes. However, it is a requirement that thematerial have a coefficient of thermal expansion that is such that thematerial is capable of expansion and contraction when heated andsubsequently cooled to an extent sufficient to perform work on a MEMSscale. Further, it is preferable that the material be resilientlyflexible. The Applicant has found that titanium aluminum nitride (TiAlN)is particularly suited for the task.

The nozzle arrangement 30 includes a motion transmitting structure 74that interconnects the working end 72 of the actuator arm 66 and theproximal end portion 76 of the paddle 54. The motion transmittingstructure 74 bridges the sealing structure 78 so that the sealingstructure 78 is interposed between at least a portion of the motiontransmitting structure 74 and the sealing structure 78.

The motion transmitting structure 74 includes an effort formation 80that extends from the working end 72 of the actuator arm 66. The motiontransmitting structure 74 also includes a load formation 82 that extendsfrom the proximal end portion 76 of the paddle 54. A lever arm formation84 interconnects the effort and load formations 80, 82. The lever armformation 84 is pivotally connected between the sidewalls 46 withconnectors in the form of opposed flexural connectors 85. The flexuralconnectors 85 are configured to experience torsional distortion uponpivotal movement of the lever arm formation 84. It will therefore beappreciated that, upon reciprocal movement of the working end 72 of theactuator arm 66, the lever arm formation 84 pivots. This pivotalmovement results in the angular displacement of the paddle 54, asdescribed above, via the load formation 82.

The motion transmitting structure 74 and the roof 42 define a slottedopening 86 that accommodates relative movement of the structure 74 andthe roof 42. The slotted opening 86 is interposed between a pair ofridges 88 that extend from the structure 74 and the roof 42. The ridges88 are dimensioned so that, when the nozzle chamber 40 is filled withthe ink 60, a fluidic seal 90 is defined between the ridges 88.Similarly, the sealing structure 78 and the proximal end portion 76 ofthe paddle 54 are configured so that a fluidic seal 92 is definedbetween the proximal end portion 76 and the sealing structure 78.

In FIGS. 3 and 4, reference numeral 100 generally indicates a nozzlearrangement of an inkjet printhead chip, in accordance with theinvention, for an inkjet printhead. With reference to FIG. 2, likereference numerals refer to like parts, unless otherwise specified.

The nozzle arrangement 100 includes nozzle chamber walls 102 positionedon the ink passivation layer 36. A roof 104 is positioned on the nozzlechamber walls 102 so that the roof 104 and the nozzle chamber walls 102define a nozzle chamber 106. The nozzle chamber walls 102 include adistal end wall 108, a proximal end wall 110 and a pair of opposedsidewalls 112. An ink ejection port 114 is defined in the roof 104 to bein fluid communication with the nozzle chamber 106. The roof 104 definesa nozzle rim 116 and a recess 118 positioned about the rim 116 toinhibit ink spread.

The walls 102 and the roof 104 are configured so that the nozzle chamber106 is rectangular in plan.

A plurality of ink inlet channels 120, one of which is shown in thedrawings, are defined through the substrate 32, the drive circuitrylayer 34 and the ink passivation layer 36. The ink inlet channel 120 isin fluid communication with the nozzle chamber 106 so that ink can besupplied to the nozzle chamber 106.

The nozzle arrangement 100 includes a motion-transmitting structure 122.The motion transmitting structure 122 includes an effort formation 124,a lever arm formation 126 and a load formation 128. The lever armformation 126 is interposed between the effort formation 124 and theload formation 128.

The nozzle arrangement 100 includes a sealing structure 130 that is fastwith the ink passivation layer 36. In particular, the sealing structure130 is composite with a primary layer 132 and a secondary layer 134. Thelayers 132, 134 are configured so that the sealing structure 130 isresiliently deformable to permit pivotal movement of the lever armformation 126 with respect to the substrate 32. The layers 132, 134 canbe of a number of materials that are used in integrated circuitfabrication. The Applicant has found that titanium aluminum nitride(TiAlN) is a suitable material for the layer 132 and that titanium is asuitable material for the layer 134.

The load formation 128 defines part of the proximal end wall 110. Theload formation 128 is composite with a primary layer 136 and a secondarylayer 138. As with the sealing structure 130, the layers 136, 138 can beof any of a number of materials that are used in integrated circuitfabrication. However, as set out above, successive deposition andetching steps are used to fabricate the nozzle arrangement 100. Itfollows that it is convenient for the layers 136, 138 to be of the samematerial as the layers 132, 134. Thus, the layers 136, 138 can be ofTiAlN and titanium, respectively.

The nozzle arrangement 100 includes an ink-ejecting member in the formof an elongate rectangular paddle 140. The paddle 140 is fixed to theload formation 128 and extends towards the distal end wall 108. Further,the paddle 140 is dimensioned to correspond generally with the nozzlechamber 106. It follows that displacement of the paddle 140 towards andaway from the ink ejection port 114 with sufficient energy results inthe ejection of an ink drop from the ink ejection port. The manner inwhich drop ejection is achieved is described in detail in the abovereferenced patents/applications and is therefore not discussed in anydetail here.

To facilitate fabrication, the paddle 140 is of TIAlN. In particular,the paddle 140 is an extension of the layer 136 of the load formation128 of the motion transmitting structure 122.

The paddle 140 has corrugations 142 to strengthen the paddle 140 againstflexure during operation.

The effort formation 124 is also composite with a primary layer 144 anda secondary layer 146.

The layers 144, 146 can be of any of a number of materials that are usedin integrated circuit fabrication. However, as set out above, successivedeposition and etching steps are used to fabricate the nozzlearrangement 100. It follows that it is convenient for the layers 144,146 to be of the same material as the layers 132, 134. Thus, the layers144, 146 can be of TiAlN and titanium, respectively.

The nozzle arrangement 100 includes an actuator in the form of a thermalbend actuator 148. The thermal bend actuator 148 is of a conductivematerial that is capable of being resistively heated. The conductivematerial has a coefficient of thermal expansion that is such that, whenheated and subsequently cooled, the material is capable of expansion andcontraction to an extent sufficient to perform work on a MEMS scale.

The thermal bend actuator 148 can be any of a number of thermal bendactuators described in the above patents/patent applications. In oneexample, the thermal bend actuator 148 includes an actuator arm 150 thathas an active portion 152 and a passive portion. The active portion 152has a pair of inner legs 154 and the passive portion is defined by a legpositioned on each side of the pair of inner legs 154. A bridge portion156 interconnects the active inner legs 154 and the passive legs. Eachleg 154 is fixed to one of a pair of anchor formations in the form ofactive anchors 158 that extend from the ink passivation layer 36. Eachactive anchor 158 is configured so that the legs 154 are electricallyconnected to the drive circuitry layer 34.

Each passive leg is fixed to one of a pair of anchor formations in theform of passive anchors 160 that are electrically isolated from thedrive circuitry layer 34.

Thus, the legs 154 and the bridge portion 156 are configured so thatwhen a current from the drive circuitry layer 34 is set up in the legs154, the actuator arm 150 is subjected to differential heating. Inparticular, the actuator arm 150 is shaped so that the passive legs areinterposed between at least a portion of the legs 154 and the substrate32. It will be appreciated that this causes the actuator arm 150 to bendtowards the substrate 32.

The bridge portion 156 therefore defines a working end of the actuator148. In particular, the bridge portion 156 defines the primary layer 144of the effort formation 124. Thus, the actuator 148 is of TiAlN. TheApplicant has found this material to be well suited for the actuator148.

The lever arm formation 126 is positioned on, and fast with, thesecondary layers 134, 138, 146 of the sealing structure 130, the loadformation 128 and the effort formation 124, respectively. Thus,reciprocal movement of the actuator 148 towards and away from thesubstrate 32 is converted into reciprocal angular displacement of thepaddle 140 via the motion transmitting structure 122 to eject ink dropsfrom the ink ejection port 114.

Each active anchor 158 and passive anchor is also composite with aprimary layer 160 and a secondary layer 162. The layers 160, 162 can beof any of a number of materials that are used in integrated circuitfabrication. However, in order to facilitate fabrication, the layer 160is of TiAlN and the layer 162 is of titanium.

A cover formation 164 is positioned on the anchors to extend over and tocover the actuator 148. Air chamber walls 166 extend between the inkpassivation layer 36 and the cover formation 164 so that the coverformation 164 and the air chamber walls 166 define an air chamber 168.Thus, the actuator 148 and the anchors are positioned in the air chamber168.

The cover formation 164, the lever arm formation 126 and the roof 104are in the form of a unitary protective structure 170 to inhibit damageto the nozzle arrangement 100.

The protective structure 170 can be one of a number of materials thatare used in integrated circuit fabrication. The Applicant has found thatsilicon dioxide is particularly useful for this task.

It will be appreciated that it is necessary for the lever arm formation126 to be displaced relative to the cover formation 164 and the roof104. It follows that the cover formation 164 and the lever arm formation126 are demarcated by a slotted opening 172 in fluid communication withthe air chamber 168. The roof 104 and the lever arm formation 126 aredemarcated by a slotted opening 174 in fluid communication with thenozzle chamber 106.

The lever arm formation 126 and the roof 104 together define ridges 176that bound the slotted opening 172. Thus, when the nozzle chamber 106 isfilled with ink, the ridges 176 define a fluidic seal during inkejection. The ridges 176 serve to inhibit ink spreading by providingsuitable adhesion surfaces for a meniscus formed by the ink.

The slotted openings 172, 174 demarcate resiliently flexible connectorsin the form of a pair of opposed flexural connectors 178 defined by theprotective structure 170. The flexural connectors 178 are configured toexperience torsional deformation in order to accommodate pivotalmovement of the lever arm formation 126 during operation of the nozzlearrangement 100. The silicon dioxide of the protective structure 170 isresiliently flexible on a MEMS scale and is thus suitable for suchrepetitive distortion.

It should be noted that the paddle 140, the sealing structure 130 andthe actuator arm 150 are discrete components. This facilitatesfabrication of the nozzle arrangement 100 while still retaining theadvantages of efficient motion transfer and sealing.

1. A nozzle arrangement for an inkjet printhead, the nozzle arrangementcomprising: a substrate assembly incorporating an electrical drivecircuitry layer and defining an ink inlet channel; a nozzle chamberstructure extending from the substrate assembly and defining a nozzlechamber in fluid communication with the ink inlet channel and an inkejection port in fluid communication with the nozzle chamber; an anchorextending from the substrate assembly; a thermal bend actuator extendingfrom the anchor and electrically coupled to the drive circuitry layer;and a lever arm coupled to the thermal bend actuator, pivotallysupported by the substrate assembly and terminating in a paddle withinthe nozzle chamber so that, upon receipt of a driving signal from thedrive circuitry layer, the thermal bend actuator bends to inducemovement of the paddle and ejection of ink in the nozzle chamber throughthe ink ejection port.
 2. A nozzle arrangement as claimed in claim 1,wherein the lever arm defines a sealing portion which forms part of anink sealing wall of the nozzle chamber structure.
 3. A nozzlearrangement as claimed in claim 1, wherein the paddle is interposedbetween the ink inlet channel ink and the ejection port.
 4. A nozzlearrangement as claimed in claim 1, wherein the nozzle chamber structuredefines a protruding rim bounding the ink ejection port.
 5. A nozzlearrangement as claimed in claim 4, wherein the nozzle chamber structurefurther defines a recess positioned about the rim to inhibit ink spread.6. A nozzle arrangement as claimed in claim 1, wherein the nozzlechamber structure is rectangular in plan.
 7. A nozzle arrangement asclaimed in claim 1, wherein the substrate assembly includes an inkpassivation layer positioned on the drive circuitry layer.